1. Field of the Invention
The present invention relates to a tape recorder which can switch a tape speed.
2. Description of the Prior Art
Tape recorders of this type generally include a recording circuit of the type shown in FIG. 1. Here, an oscillation block OSCB is connected to a magnetic head HD. This oscillation block OSCB has one end of a primary winding of an oscillation transformer T connected to a base of a transistor Tr through a resistance R.sub.1 and the other end connected to a collector of the same transistor Tr. This transistor Tr has a grounded emitter. A capacitor C.sub.1 is connected between both terminals of the secondary winding of the oscillation transformer T. One end of the parallel combination of the secondary winding and the capacitance C.sub.1 is connected to the head HD and the other end thereof is connected to the emitter of the transistor Tr through a capacitor C.sub.2.
The center tap of the primary winding of the oscillation transformer T connects to a power supply source (not shown) through a bias resistance BR. The bias resistance BR is composed of resistances R.sub.2 and R.sub.3, so that when a tape speed is 1.2 cm/sec, the resistance R.sub.2 is only connected in parallel, and when the tape speed is 2.4 cm/sec, the resistance R.sub.3 is connected in parallel, respectively, so as to generate a higher AC bias from the oscillation block OSCB. The switching of the resistances R.sub.2 and R.sub.3 in this case is carried out by a switch SW interlocked with speed switching of the motor (not shown).
The oscillation block OSCB receives the output of a final stage amplifier AMP through an equalizing circuit EQ. The equalizing circuit EQ is formed by connecting the resistance R.sub.5 in series with a parallel combination of the resistance R.sub.4 and the capacitor C.sub.3 and set at a given time constant.
According to this construction, the optimum AC bias in response to the tape speed can be obtained, and under this state, the recording output of the amplifier is applied to the head HD through the equalizing circuit EQ to record the tape.
With such a construction, however, because the time constant of the equalizing circuit EQ is the same when the tape speed is 1.2 cm/sec and 2.4 cm/sec, the frequency characteristics become different. In particular, at 2.4 cm/sec, the frequency characteristic is extended to a higher range to produce a strain in high tones, and as a result, as compared with the case of 1.2 cm/sec, tone quality becomes considerably different.